Solution for clearing LED epoxy on emitter?

Thread Starter

Steveggz

Joined Oct 17, 2017
4
I managed to get rosin flux on several surface mount Cree XT-E led's which has caused the clear plastic/epoxy coating on the emitter to become frosted and unclear. I tried several methods of cleaning with no success. Is there some sort of lacquer or epoxy I can use to coat it and make it clear?
 

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jpanhalt

Joined Jan 18, 2008
9,771
Hi Steve,

You have left out some information from another post that might be relevant:
Steve @ elsewhere said:
I've tried everything from 91% alcohol and scrubbing to acetone and even polishing it with a dremmel and buffing wheel.
The solvents and abrasives you have used probably etched or fogged the "epoxy" or whatever plastic is used as a lens. You could try a clear coating. Clear acrylic lacquer or automotive clear coat might help. Even clear floor wax might help but would be less permanent. Don't know how hot that lens gets,. You might need something more heat stable than acrylics.

I use absolute ethanol to remove excess rosin flux. It does not affect most plastics. I suspect the 91% "alcohol" you used was isopropyl alcohol (aka isopropanol, 2-propanol). I have had poorer luck with that. Unfortunately, the harsher solvents you also used may decrease the life expectancy of the lens by causing cracking or crazing in the long term.

At this point, the best suggestion I can give is to start over with a new led. Aluminum foil or even masking tape will make a good splash guard.

John
 

Alec_t

Joined Sep 17, 2013
11,416
Is a slightly etched/fogged lens such a bad thing? It will help to disperse the light, which is normally an advantage. No one will be looking directly at the LED when it is on.
 

Thread Starter

Steveggz

Joined Oct 17, 2017
4
Hi Steve,

You have left out some information from another post that might be relevant:


The solvents and abrasives you have used probably etched or fogged the "epoxy" or whatever plastic is used as a lens. You could try a clear coating. Clear acrylic lacquer or automotive clear coat might help. Even clear floor wax might help but would be less permanent. Don't know how hot that lens gets,. You might need something more heat stable than acrylics.

I use absolute ethanol to remove excess rosin flux. It does not affect most plastics. I suspect the 91% "alcohol" you used was isopropyl alcohol (aka isopropanol, 2-propanol). I have had poorer luck with that. Unfortunately, the harsher solvents you also used may decrease the life expectancy of the lens by causing cracking or crazing in the long term.

At this point, the best suggestion I can give is to start over with a new led. Aluminum foil or even masking tape will make a good splash guard.

John
Thanks for information. I think replacing the LED's might be the best option although I messed up more than I thought. Looking closer I've now noticed about 11 LED's have some sort of permanent fogginess.

I'll try straight ethanol, I have a bottle of Everclear that hast been touched in years just to see if their still salvageable. I'm also going to look into a high temp non yellowing lacquer and do a test sample just for fun.
 

Thread Starter

Steveggz

Joined Oct 17, 2017
4
Is a slightly etched/fogged lens such a bad thing? It will help to disperse the light, which is normally an advantage. No one will be looking directly at the LED when it is on.
It's funny you mention that, after reading up on LED's I found they actually make some with a foggy lens for that exact reason. I am just hoping it wont reduce the light output but just disperse it differently. Do you know the answer to that? It's ultimately going to be (104 Cree royal blue LED's) behind a remote phosphor plate.
 

jpanhalt

Joined Jan 18, 2008
9,771
Hi Steve,

I had to look up "Everclear." Apparently, its highest proof is 190 (i.e., 95%), which implies it is the water azeotrope of ethanol, just as 91% isopropyl alcohol is the water azeotrope. In non-chemist terms, those are the highest concentrations you can get by simple distillation of water mixtures. Absolute ethanol is 100% or very close to it. That little bit of water can make a huge difference in solvent potency for larger organic molecules like abietic acid and related compounds in rosen flux. Frankly, I have never tried 95% ethanol, as I have the absolute stuff readily available. It may work. You can try a test surface. Also, in my experience, it is easier to remove fresh flux residue than it is after a week or so.

Rather than Everclear, a denatured ethanol may work. There are lots of formulas for that and they vary by country as it is regulated in most places. Ethanol + methanol formula is probably OK as are many of the others. The little bit of bitterant that is frequently added shouldn't make much difference.
 

ebp

Joined Feb 8, 2018
2,332
If you used acetone, chances are the damage is permanent. Acetone is an effective spot cleaner for flux, but great care is required.

Rosin-based flux is readily removed with 99% isopropanol, provided it has not been overheated (that applies regardless of solvent). Depending on where you live it is a common drug store item (caution - so is 70%) and likely to be very much less expensive than Everclear. Do not waste your money on the 99.xxxx% isopropanol from companies like MG Chemicals.

I've cleaned a great many boards with a 3-bath system with isopropanaol. The first bath removes the bulk of the flux and becomes heavily contaminated. The second bath, after a brief drain, leaves the board reasonably clean. I sometimes use a bath the third step, sometimes rinse with fresh alcohol from a wash bottle. For SMD it often use a compressed air blow-off then another clean rinse. The baths are "moved up" as they become contaminated. Regardless of what you use for a solvent it is necessary to use multiple steps to get the board clean. Some spray-can board cleaner manufacturers like to tell you about how quickly the solvent evaporates. That is exactly what you don't want for effective cleaning. Some spray can cleaners contain solvents that can "poison" aluminum electrolytic capacitors.

Water based saponifier solutions are also effective for rosin flux.

With any opto component the manufacturer's notes on cleaning should be followed. The encapsulants are not, in general, as solvent resistant as those for many other components.

My preference, where workable, is to use water soluble flux. Such fluxes are readily removed with warm water, but must be removed within a few hours because they are corrosive and the corrosion products are very difficult to remove.

Cleaning surface mount boards is substantially more difficult because of entrapment of the solvent under the components. Pressure impingement is necessary.
 

takao21203

Joined Apr 28, 2012
3,695
Do not even contemplate using butane for removal of flux. I can think of few things more stupid.
Why? I have done it sometimes works quite well. Butane is a pretty good solvent. And just vaporates off quite quickly.
Otherwise need larger amounts of gasoline but can dillute gasoline remains (which still have flux solved in them) with butane, so need only small amounts two times.
 

takao21203

Joined Apr 28, 2012
3,695
Of course I can not really recommend it, obviously if you have a spark you get a problem. But small amounts in a reasonably large room do absolutely nothing, similar to refilling a lighter.
 

ebp

Joined Feb 8, 2018
2,332
Butane is extremely volatile and highly flammable which makes it extremely dangerous, foolish to use and grossly irresponsible to recommend.

It is also a very poor choice for a cleaning solvent specifically because it is so volatile. In order for a solvent to do a good job of cleaning flux from a circuit board the solution of flux in solvent must be physically removed from the board. If the solvent evaporates it leaves the flux behind and nothing worthwhile is accomplished.

[EDIT] Butane is also non-polar, which makes is a very poor solvent for the activators in rosin flux, which are really the only reason to remove the flux in the first place.
 
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takao21203

Joined Apr 28, 2012
3,695
well i have used it and it works quite well, first some gasoline (lighter fluid) to dissolve the flux and then wash with butane, also has high pressure.
 

ericgibbs

Joined Jan 29, 2010
10,205
hi,
It is highly likely the 'corrosive flux' the TS used for soldering, has interacted with LED's clear plastic cover, causing a ' frosting' of the clear plastic, it is not going to be easily wiped off with solvents.
E
 

takao21203

Joined Apr 28, 2012
3,695
isopropanol / Acetone causes many plastic kinds to become opaque and brittle, and quick, and doesnt go away

Its efficient to degrease metal surfaces but not appropiate for components.
 

shortbus

Joined Sep 30, 2009
7,766
hi,
It is highly likely the 'corrosive flux' the TS used for soldering, has interacted with LED's clear plastic cover, causing a ' frosting' of the clear plastic, it is not going to be easily wiped off with solvents.
E
Glad you brought the discussion back to the topic. How about using one of the many car headlight cleaners/restorers on the leds? something like these - https://www.amazon.com/Best-Sellers-Automotive-Headlight-Restoration-Kits/zgbs/automotive/2687788011
 
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